With the recent popularity of the Internet, the number of users who exchange various data with other users over the Internet has increased.
However, for example, when a user is to transmit a certain image to the device of another user, traditionally, the image data cannot be transmitted in a stable manner due to the difference between the transmission speed of the transmission path to which the device of the other user is connected and the transmission speed of the transmission path to which the device of the user is connected.
An approach in which a data transmission device detects network congestion from the delayed arrival of packets to control the data transmission rate based on the detection has been proposed (see, for example, Japanese Unexamined Patent Application Publication No. 11-308271).
However, the approach described in Japanese Unexamined Patent Application Publication No. 11-308271 suffers from the problem that the actual data speed cannot be determined until data transmission and reception start.